Optical memory technology has gained prevalence, where optical disk media are employed as high-density and large-capacity storage media for recording data such as video, audio, text, programs, etc. Particularly prevalent are DVDs (Digital Versatile Discs), CDs (Compact Disc), and the like, which have pit patterns. This optical memory technology uses a finely-converged light beam to record data onto an optical disk medium with a high precision and reliability.
The principle of recording will be briefly described. For example, in the case where data is to be recorded onto an optical disk medium having a phase-changeable material, the optical disk medium is irradiated with light which is modulated in pulse form, at a power which is higher than that during reproduction, thus causing the phase-changeable material to go through intermittent phase changes. As a result, a changing pattern of reflectance of the phase-changeable material is created, whereby data recording is performed.
During reproduction, the optical disk medium is irradiated with a low power of light which will not cause phase changes in the phase-changeable material, thus detecting a changing pattern of reflectance of the phase-changeable material, whereby data is reproduced.
Such recording/reproduction operations are performed by an optical pickup device. Functions of an optical pickup device are generally classified into: formation of a diffraction-limited minute spot by converging light which is output from a light source; focusing control; tracking control; detection of a pit signal; and so on. These functions are realized with a combination of various optics and approaches of photoelectric conversion/detection, which is made in accordance with the purpose and application.
In order to allow light to be converged down to a diffraction limit, semiconductor laser elements are generally used as light sources. Thus, a small semiconductor laser element is mounted in an optical pickup device.
With an expansion in the applications of optical disk media, optical disk medium formats for higher recording densities have been developed, and the light spot to be formed during data recording/reproduction has become even smaller in size. The size of a light spot of laser light is in inverse proportion to the NA of an objective lens which is used for convergence, and is in proportion to the wavelength of the laser light. Therefore, in order to obtain a minute light spot size, the wavelength of laser light has been reduced.
Thus, in a situation where optical disk media for higher recording densities are being developed, from the standpoint of effectively utilizing the data and resources which a user may have acquired in the past, an optical disk apparatus is required to be able to perform recording/reproduction for a plurality of types of optical disk media of respectively different formats.
One technique of supporting a plurality of formats is to mount a plurality of optical pickup devices in an optical disk apparatus. However, in terms of downsizing of the apparatus, it is desirable if a single optical pickup device can support a plurality of formats. This makes it necessary to mount on a single optical pickup device a plurality of semiconductor laser elements of respectively different oscillation wavelengths, and also mount a plurality of photodetectors that correspond to the respective semiconductor laser elements and a plurality of actuators, etc., for controlling the positions of the optical elements with a high precision corresponding to a high recording density.
This has led to an increase in the number of circuit wiring lines for allowing signals to be input to or output from an optical pickup device, which also necessitates an increase in the space occupied by them within the optical disk apparatus. This results in problems such as constraints on the placement of parts, and deterioration of signals and limitations on current-carrying capacity due to narrower pitches of wiring patterns.
In order to address such problems, a technique of reducing the number of signal lines to be taken out from the optical pickup device is disclosed in Patent Document 1.
From the optical pickup device of Patent Document 1, wiring lines which are used only at the time of making adjustments for the device during production are taken out. An adjustment circuit which makes adjustments for the device is connected to the wiring lines for adjustment purposes.
When making adjustments for the optical pickup device, the wiring lines for adjustment purposes are used to supply adjustment signals to the optical pickup device, and various adjustments are performed, e.g., position adjustment and characteristic adjustment for the respective component elements. After the adjustments, the wiring lines which are needed only for the adjustments are cut at a point near an end of the optical pickup device. By cutting off the wiring lines which are needed only for the adjustments, the number of wiring lines to be taken out from the optical pickup device can be reduced.    [Patent Document 1] Japanese Laid-Open Patent Publication No. 2005-85299